Metal‐Free‐Porphyrin‐Catalyzed Oxygen Reduction at Liquid–Liquid Interfaces

Catalysis of Oxygen Reduction by Metal-Free Porphyrins in One- and Two-Phase Liquid Systems

“…96 The relative catalytic capability of various porphyrin free bases towards oxygen reduction by Fc and Me 2 Fc at the polarized water/1,2-DCE interface was assessed by comparing the magnitudes of the catalytic currents, the rate of the production of Fc + or Me 2 Fc + , and the rate of the formation of H 2 O 2 . 101 In this way, the catalytic capability of three substituted H 2 TPP porphyrins was shown to follow the order: H 2 TPPNO 2 > H 2 TPP > H 2 TPPOCH 3 ; i.e., the porphyrins bearing functional groups having a greater electron-withdrawing nature exhibit a stronger catalytic effect. 101 It is noteworthy that the oxidation potentials of these porphyrins follow the same order (see Section III), i.e., H 2 TPPNO 2 , which exhibits the highest catalytic capability, is the weakest reducing agent.…”

“…101 In this way, the catalytic capability of three substituted H 2 TPP porphyrins was shown to follow the order: H 2 TPPNO 2 > H 2 TPP > H 2 TPPOCH 3 ; i.e., the porphyrins bearing functional groups having a greater electron-withdrawing nature exhibit a stronger catalytic effect. 101 It is noteworthy that the oxidation potentials of these porphyrins follow the same order (see Section III), i.e., H 2 TPPNO 2 , which exhibits the highest catalytic capability, is the weakest reducing agent. This observation supports an activation pathway 19,96 involving the binding of O 2 to the porphyrin diacid through a NH + ...O 2 hydrogen bond, followed by a polarization of the O-O bond, rather via a redox pathway that is typical for catalysis by metalloporphyrins.…”

“…In particular, cyclic voltammetry was used to evaluate acid dissociation constants for protonated 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H 2 FAP), 96 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (H 2 TPPOCH 3 ) and 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin (H 2 TPPNO 2 ). 101 Table 4 summarizes the pK a values of the mono-and di-protonated porphyrin free bases. It can be seen that H 2 TPPOCH 3 , which bears electron-donating -OCH 3 groups, is more easily protonated than H 2 …”

Electrochemistry-mass spectrometry for mechanism study of oxygen reduction at water/oil interface

“…ORR is of utmost importance in advanced electrochemical energy conversion22. ORR at L/L interfaces has been widely studied using various lipophilic electron donors, e.g., ferrocene (Fc), DMFc, TTF, etc723242526. Compared to other complicated reaction systems, ORR at water/1,2-dichloroethane (DCE) interfaces catalyzed by metal-free porphyrin, tetraphenylporphyrin (H 2 TPP), has been explored thoroughly2526.…”

“…ORR at L/L interfaces has been widely studied using various lipophilic electron donors, e.g., ferrocene (Fc), DMFc, TTF, etc723242526. Compared to other complicated reaction systems, ORR at water/1,2-dichloroethane (DCE) interfaces catalyzed by metal-free porphyrin, tetraphenylporphyrin (H 2 TPP), has been explored thoroughly2526. The possible mechanism of two consecutive protonations of H 2 TPP leading to the coordination of porphyrin diacid by molecular O 2 and reduction of oxygen was proposed and supported by cyclic voltammetry, UV-visible spectrometry, and model calculation2325.…”